.\"	$OpenBSD: dir.5,v 1.6 1999/05/23 14:11:04 aaron Exp $
.\"	$NetBSD: dir.5,v 1.5 1995/03/28 17:30:20 jtc Exp $
.\"
.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\"
.\"     @(#)dir.5	8.3 (Berkeley) 4/19/94
.\"
.Dd April 19, 1994
.Dt DIR 5
.Os
.Sh NAME
.Nm dir , dirent
.Nd directory file format
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/dir.h>
.Sh DESCRIPTION
Directories provide a convenient hierarchical method of grouping
files while obscuring the underlying details of the storage medium.
A directory file is differentiated from a plain file
by a flag in its
.Xr inode 5
entry.
It consists of records (directory entries) each of which contains
information about a file and a pointer to the file itself.
Directory entries may contain other directories
as well as plain files; such nested directories are referred to as
subdirectories. 
A hierarchy of directories and files is formed in this manner
and is called a file system (or referred to as a file system tree).
.\" An entry in this tree,
.\" nested or not nested,
.\" is a pathname.
.Pp
Each directory file contains two special directory entries; one is a pointer
to the directory itself
called dot
.Pq Dq \&.
and the other a pointer to its parent directory called dot-dot
.Pq Dq \&.. .
Dot and dot-dot
are valid pathnames, however,
the system root directory
.Pq Dq / ,
has no parent and dot-dot points to itself like dot.
.Pp
File system nodes are ordinary directory files on which has
been grafted a file system object, such as a physical disk or a
partitioned area of such a disk (see
.Xr mount 8 ) .
.Pp
The directory entry format is defined in the file
.Aq Pa dirent.h :
.Bd -literal
#ifndef _DIRENT_H_
#define _DIRENT_H_

/*
* A directory entry has a struct dirent at the front of it, containing its
* inode number, the length of the entry, and the length of the name
* contained in the entry.  These are followed by the name padded to a 4
* byte boundary with null bytes.  All names are guaranteed null terminated.
* The maximum length of a name in a directory is MAXNAMLEN.
*/

struct dirent {
	u_long	d_fileno;	/* file number of entry */
	u_short	d_reclen;	/* length of this record */
	u_short	d_namlen;	/* length of string in d_name */
#ifdef _POSIX_SOURCE
	char	d_name[MAXNAMLEN + 1];	/* maximum name length */
#else
#define MAXNAMLEN       255
	char    d_name[MAXNAMLEN + 1];  /* maximum name length */
#endif

};

#ifdef _POSIX_SOURCE
typedef void *	DIR;
#else

#define	d_ino		d_fileno	/* backward compatibility */

/* definitions for library routines operating on directories. */
#define	DIRBLKSIZ	1024

/* structure describing an open directory. */
typedef struct _dirdesc {
	int	dd_fd;    /* file descriptor associated with directory */
	long	dd_loc;	  /* offset in current buffer */
	long	dd_size;  /* amount of data returned by getdirentries */
	char	*dd_buf;  /* data buffer */
	int	dd_len;   /* size of data buffer */
	long	dd_seek;  /* magic cookie returned by getdirentries */
} DIR;

#define	dirfd(dirp)	((dirp)->dd_fd)

#ifndef NULL
#define	NULL	0
#endif

#endif /* _POSIX_SOURCE */

#ifndef _KERNEL

#include <sys/cdefs.h>

#endif /* !_KERNEL */

#endif /* !_DIRENT_H_ */
.Ed
.Sh SEE ALSO
.Xr fs 5 ,
.Xr inode 5
.Sh HISTORY
A
.Nm
file format appeared in
.At v7 .